Mayfly Groups

Mayflies are sometimes divided into four groups based on the behavior of the nymphs.

Group 1

Group II

Crawlers

Swimmers

Clingers

Burrowers

Group I mayfly nymphs have a front section � from beginning of head to rear edge of wing pad � that is as large or larger than the rear section � from end of wing pad to end of abdomen.

Crawler � The width of the head includes eyes is similar or equal to the width of the abdomen, excluding the gills.

Clinger � The width of the head including eyes is always wider than the width of the abdomen, excluding gills.

Group II mayflies nymphs have a front section, from the beginning of the head to the rear edge of the wing pad, that is smaller than the rear section, from the end of the wing pad to the end of the abdomen.